You’re staring at your aquarium. It’s late. Everything is quiet. And there’s your fish, floating calmly, fins moving slowly, eyes wide open. Are they... asleep? Or just zoning out? Fish don’t come ...

Fish don’t have eyelids. They don’t curl up in beds or snore, so it’s easy to assume they just keep swimming forever without rest. But they do sleep—it just looks very different from how we do it.

Sleep in fish may look different from humans, but rest is essential for survival. Here’s what experts have to say about fish sleep. A protective mucous cocoon surrounds this parrotfish as it sleeps in ...